Novel Optical Frequency Combs Injection Locking Architectures

Due to their highly stable timing characteristics, optical frequency combs have become instrumental in applications ranging from spectroscopy to ultra-wideband optical interconnects, high-speed signal processing, and exoplanet search. In the past few years, there has been a necessity for frequency combs to become more compact, robust to environmental disturbances, and extremely energy efficient, where photonic integration shows a clear pathway to bring optical frequency combs to satellites, airships, drones, cars, and even smartphones. Therefore, the development of chip-scale optical frequency combs has become a topic of high interest in the optics community. This dissertation reviews the work made in the field of chip-scale optical frequency combs using optically injection locked semiconductor mode-locked lasers. First it shows the efforts in the design, characterization and calibration of several semiconductor mode-locked laser architectures on an InP-based platform. Then two separate efforts to obtain a self-referenced optical frequency comb are described. The first one based on an InP-based MLL-PIC that is enhanced via COEO multi-tone injection locking, and then amplified and broadened to an octave using pulse picking and a combination of bulk and integrated nonlinear optics. The second approach is based on the synchronization of two lasers via regenerative harmonic injection locking, one with a repetition rate in the microwave regime (10s of GHz) and another one in the THz domain (100s of GHz), first utilizing an electro-optic modulated comb and then an integrated SiN microresonator-based Kerr frequency comb. This manuscript envisions future work to achieve an optical to RF link using optical injection locking architectures with long-term stabilization and the outlook of using this technique in conjunction with octave-spanning microresonator-based Kerr combs to achieve a self-referenced chip-scale optical frequency comb

Towards On-Chip Self-Referenced Frequency-Comb Sources Based on Semiconductor Mode-Locked Lasers.

Miniaturization of frequency-comb sources could open a host of potential applications in spectroscopy, biomedical monitoring, astronomy, microwave signal generation, and distribution of precise time or frequency across networks. This review article places emphasis on an architecture with a semiconductor mode-locked laser at the heart of the system and subsequent supercontinuum generation and carrier-envelope offset detection and stabilization in nonlinear integrated optics

Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world

Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic. Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality. Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States. Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis. Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection

Stable Electro-Optic Frequency Comb Generation Using An Ultrahigh Finesse Etalon Filtered Optoelectronic Oscillator

In this work we investigate the overall stability of tunable, broadband electro-optic frequency combs created in an optoelectronic oscillator filtered with an ultra-high finesse Fabry-Perot etalon. Fractional frequency stability measurements show Allan deviations as low as 3E-13 for the comb central frequency of 193THz, and as low as 5E-10 on the 10.5GHz repetition frequency. At timescales of τ = 0.1s, the total frequency fluctuation of the outermost comb lines is calculated to be on the order of 388Hz. Individual comb line amplitude stability is also investigated, and the average amplitude fluctuation amongst all comb lines within 10dB amplitude deviation is measured to be ± 0.22dB standard deviation

Tunable Broadband Electro-Optic Comb Generation Using An Optically Filtered Optoelectronic Oscillator

Tunable electrooptic combs are generated in an optoelectronic oscillator that is optically filtered using a 100 000 finesse Fabry-Pérot etalon. Optical and electrical outputs of the oscillator are combined in a series of external phase modulators to generate spectrally flat, broadband optical combs. Adjustment of a variable delay in the oscillator allows for tuning of output combline spacing to harmonics of the etalon\u27s 1.5-GHz free spectral range. Experimental results demonstrate regeneratively created electrooptic combs whose comb teeth spacing can be tuned to 7.5, 9, 10.5, and 12 GHz, with center comb tooth linewidths on the order of hundreds of Hertz. In the best case, the output electrooptic modulation comb consists of 52 individual comblines within a 10-dB amplitude deviation over a span of approximately 5 nm. Linear pulse compression is used to demonstrate ultrashort pulses with a 2.6-ps autocorrelation pulse width at a repetition rate of 10.5 GHz

An Integrated Racetrack Colliding-Pulse Mode-Locked Laser With Pulse-Picking Modulator

We present a novel racetrack colliding-pulse mode-locked laser with external pulsepicking and optical amplification monolithically integrated on InP. Optical pulses with FWHM of 2.36 ps are observed under hybrid mode-locking at 10 GHz repetition rate

Electro-Optic Comb Generation From Noise With A Photonically Filtered Optoelectronic Oscillator

We present a novel architecture for electro-optic comb generation by utilizing both optical and RF outputs of a photonically filtered optoelectronic oscillator. The output is an EO comb with 10.5 GHz combline spacing generated entirely from noise without an external driving RF signal

Tunable Broadband Electro-Optic Comb Generation Using an Optically Filtered Optoelectronic Oscillator

Tunable electrooptic combs are generated in an optoelectronic oscillator that is optically filtered using a 100 000 finesse Fabry-Pérot etalon. Optical and electrical outputs of the oscillator are combined in a series of external phase modulators to generate spectrally flat, broadband optical combs. Adjustment of a variable delay in the oscillator allows for tuning of output combline spacing to harmonics of the etalon\u27s 1.5-GHz free spectral range. Experimental results demonstrate regeneratively created electrooptic combs whose comb teeth spacing can be tuned to 7.5, 9, 10.5, and 12 GHz, with center comb tooth linewidths on the order of hundreds of Hertz. In the best case, the output electrooptic modulation comb consists of 52 individual comblines within a 10-dB amplitude deviation over a span of approximately 5 nm. Linear pulse compression is used to demonstrate ultrashort pulses with a 2.6-ps autocorrelation pulse width at a repetition rate of 10.5 GHz

An Integrated Racetrack Colliding-Pulse Mode-Locked Laser With Pulse-Picking Modulator

We present a novel racetrack colliding-pulse mode-locked laser with external pulsepicking and optical amplification monolithically integrated on InP. Optical pulses with FWHM of 2.36 ps are observed under hybrid mode-locking at 10 GHz repetition rate

Regenerative Multi-Tone Injection Locking For Linewidth Enhancement And Repetition Rate Stabilization Of A Pic Mode-Locked Laser

We report the stabilization of a 10 GHz monolithic passively mode-locked laser using a novel combination of multi-tone injection locking and regenerative mode-locking via optoelectronic loop. Comb-teeth linewidths are narrowed by 4000x and repetition rate is stabilized to better than 10-10/τ at 1 second